HS Tarm draft fan question

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Mar 1, 2008
I have a HS Tarm Solo Plus 30 MK ll question. I would like to replace my AC draft fan with a DC draft fan so that I could use a VFD to control the fan speed based on the boiler temp.. I can not find what the AC draft CFM is. Anyone know what the stock CFM is on the draft fan?


Minister of Fire
Jan 1, 2008
Northern MN
This may answer your question. I have a Solo Plus 40. The draft fan has an adjustable damper under the top cover. The result is that I'm sure there is a maximum CFM with the damper wide open and very low to no CFM with the damper completely closed. That being said, I think this may be a replacement for the Tarm blower, and specs show 152 CFM.

In addition, I'm not sure adjusting the fan speed is really what you want, unless the adjustment is intended always to provide the CFM which results in the most efficient burn, and boiler water temp is only one variable to be considered to achieve that goal.

For my Tarm I installed a temperature controller with a K-type sensor in the flue that shuts the draft fan off if flue temperature exceeds a maximum and turns it back on when flue temp drops below the maximum. My intent was simply to prevent excessively high flue temp. It works very well.